Zach Amsden c87ab35af1 IMPALA-4813: Round on divide and multiply ...

Address rounding on divide and multiply when results are truncated.

Testing: Manually ran some divides that should overflow, then added
the results to the test.  Made the decimal-test use rounding behavior
by default, and now the error margin of the test has decreased.

Initial perf results:

Multiply is totall uninteresting so far, all implementations
return the same values in the same time:

+-------------------------+-----------------------------------+
| sum(l_quantity * l_tax) | sum(l_extendedprice * l_discount) |
+-------------------------+-----------------------------------+
| 61202493.3700           | 114698450836.4234                 |
+-------------------------+-----------------------------------+
Fetched 1 row(s) in 1.13s

Divide shows no regression from prior with DECIMAL_V2 off:

+-----------------------------+-----------------------------------+
| sum(l_quantity / l_tax)     | sum(l_extendedprice / l_discount) |
+-----------------------------+-----------------------------------+
| 46178777464.523809516381723 | 61076151920731.010714279183910    |
+-----------------------------+-----------------------------------+
before:  Fetched 1 row(s) in 13.08s
after:   Fetched 1 row(s) in 13.06s

And with DECIMAL_V2 on:

+-----------------------------+-----------------------------------+
| sum(l_quantity / l_tax)     | sum(l_extendedprice / l_discount) |
+-----------------------------+-----------------------------------+
| 46178777464.523809523847285 | 61076151920731.010714285714202    |
+-----------------------------+-----------------------------------+
Fetched 1 row(s) in 16.06s

So the performance regression is not as bad as expected.  Still,
divide performance could use some work.

Change-Id: Ie6bfcbe37555b74598d409c6f84f06b0ae5c4312
Reviewed-on: http://gerrit.cloudera.org:8080/6132
Reviewed-by: Dan Hecht <dhecht@cloudera.com>
Tested-by: Impala Public Jenkins

2017-03-02 20:12:05 +00:00

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